1. Field of the Invention
The present invention relates to a method of and an apparatus for magnetically transferring a pattern of magnetic information on a master disc to a slave disc to be used as a magnetic recording medium in disc drives such as hard disc drives and floppy disc drives, and to a magnetic recording medium with magnetic information recorded thereon.
2. Description of Related Art
In recent years, in a distribution system of magnetic discs such as hard discs for use with rapidly widespread hard disc drives, it is the common practice to magnetically write various information, e.g. format information and address information on such a magnetic disc before installing the magnetic disc into a disc drive in a disc drive production site alter delivery from the disc manufacturer. Although the information writing can be performed by use of a magnetic head, it is preferred in terms of efficiency of writing to employ a master disc with magnetic information including format and address information magnetically written therein for performing blanket magnetic transfer of the magnetic information to the magnetic disc.
In performing of the blanket magnetic transfer, a slave disc (magnetic disc) is held tight between two master discs supported by recessed disc holders, respectively, by moving one of the disc holders to the other. Then, a space formed between the recessed disc holders is sealed up by an O-ring as a sealing member to provide an air-tight chamber. In this sealed state, air in spaces around inner and outer peripheries of the discs in contact in the air-tight chamber is evacuated sufficiently enough to bring the master discs and the slave disc into intimate contact with one another without any air gap between contact surfaces of the discs due to residual air. In this way, the slave disc is firmly held between the two master discs in intimate contact. This holding manner facilitates simplified, reliable magnetic transfer.
However, when implementing such evacuation of air from the spaces formed around the inner and outer peripheries of the discs in contact in the air-tight chamber by means of vacuum suction, holding power acting on the discs in contact is reduced, so that the discs tend to move relatively to one another and, in consequence, loose coaxial alignment. If the slave disc is out of coaxial alignment with the master discs, a pattern of magnetic information is at risk of being off-centrally transferred on the slave disc. In particular, in the case where the slave disc is held by the master discs without contact with anything else in terms of prevention of contamination, air is constantly evacuated from the air-tight chamber. In consequence, the slave disc is locally subjected to negative pressure, so as to tend to cause displacement relative to the master discs. Furthermore, when opening the air-tight chamber by moving one of the disc holders away from the other, the slave disc held on the other disc holder is apt to be dragged by the master disc held on the moving disc holder due to mutual adhesion of mirror finished surfaces of the slave and master discs. This incurs the risk of irregular stop of the magnetic transfer apparatus.
It is therefore an object of the present invention to provide a method and an apparatus for magnetic transfer which prevents an occurrence of relative displacement between master and slave discs during evacuation of air from an air-tight chamber formed between disc holders and also prevents the slave disc from being dragged by the master disc during opening the air-tight chamber and further to provide a magnetic recording medium to which magnetic information has been transferred from the master disc by use of the magnetic transfer method and apparatus.